The present invention relates to solutions of aluminum citrate.
Aluminum citrate solutions have been found useful for crosslinking polymers such as carboxymethylcellulose (CMC) or partially hydrolyzed polyacrylamide. The phenomenon has found application in enhanced oil recovery processes. An example of such is disclosed in U.S. Pat. No. 3,762,476. The in situ gelling of the polymers results in blocking of highly permeable zones which can allow one to recover oil which otherwise could not be recovered by conventional means.
In the past, dilute solutions have been prepared in the field by dissolving aluminum sulfate and sodium citrate in water. If the concentration of such solutions is increased, it has been noted that in some formations precipitates formed as a result of interaction between the sulfate ions and alkaline earth metal cations in the formation or in the water employed. Such precipitations have been found undesirable since they can result in formation blockages where they are not wanted.
In view of the large quantities of aluminum citrate that are employed in such enhanced oil recovery processes, it is obviously desirable to be able to have available stable, highly concentrated solutions that are substantially free of particulate matter. It is generally desired to have an aluminum citrate solution which, after 100 hours at 100.degree. F., will not contain over about 3 weight percent of solid precipitates. Some such solutions have in the past been made by reacting aluminum chloride, citric acid, and either ammonia or sodium hydroxide.
The present invention provides an alternative method for preparing stable aqueous aluminum citrate solutions. In some embodiments, it is possible to produce aluminum citrate compositions economically competitive with those produced from aluminum chloride.